The long term objective of this research is to elucidate the mechanism(s) by which steroid hormones regulate uterine blood flow. Our previous findings have shown that uterine blood flow is dependent primarily on uterine arterial tone, rather than on phasic contractility. Our recent studies have linked uterine arterial tone to the activity of protein kinase-C. Thus, the proposed research will examine the factors controlling the activity of protein kinase-C (PKC): the synthesis and intracellular redistribution of PKC, the availability of membrane diacylglycerol, the source of the Ca++ which activates the enzyme, and the mechanism by which estrogen-stimulated peroxidases modify PKC activity. The experiments proposed to investigate each of these factors are designed to test the hypothesis that: Uterine blood flow and tone are regulated by the phosphorylation of specific intracellular proteins by PKC. The activity of PKC is dependent upon 1) the availability of diacylglycerol in the smooth muscle membrane, and 2) calcium entering the cell through the potential sensitive calcium channels (PSC). Estrogen decreases uterine arterial tone by restricting the amount of Ca++ entering the cell to activate PKC. The action of estrogen is indirect, and involves increases in peroxidases in the uterus. The peroxidases have a dual effect on PKC/tone: the enzyme converts the estrogen to catechol estrogen, which blocks the uptake of Ca ++ via the PSC, and it catabolizes the endogenous agonist which generates tone, epinephrine. Exploration of this hypothesis will utilize a multidisciplinary approach and will draw upon the investigators' expertise in the fields of Animal Science (Reproduction), Obstetrics/Gynecology, Biochemistry, Anatomy, Medicinal Chemistry and Enzymology. Although the rat, cow, and pig are the animals under study, the research should have extensive application in human medicine. Certainly the results should help understand the mechanisms underlying pathologic conditions characterized by insufficient uterine blood flow: Infertility, abortion, intrauterine growth retardation and toxemia of pregnancy. Since a Medicinal Chemist collaborates on this study, there is an opportunity to design and synthesize the drugs needed to restory uterine blood flow to normalcy.